August 6, 2025

Scrubbers and the Changing Currents of Maritime Compliance

The maritime industry is large and complex, and much like the ships themselves, it takes time to turn around. Decisions shaped by complex logistical networks, significant capital investments, and operating models built around tight margins create a momentum that is difficult to overcome. In one recent survey, more than a third of maritime professionals admitted they were “actively resistant to change.” Given the structure of the industry, this caution is unsurprising.

However, external conditions are changing rapidly, and this resistance threatens to leave the industry unprepared. Environmental risks are becoming more severe, and regulatory frameworks are growing more stringent. While profitability has traditionally been the primary driver of decision-making in shipping, environmental considerations are now becoming increasingly important. With that said, asset owners will, as they always have, focus on how to optimize the value of their asset, in the case of shipowners, this is often a matter of having the lowest operating costs or lowest fuel consumption, where installing a scrubber can be seen somewhat as a trade-off between the two.

Scrubbers, or exhaust gas cleaning systems, have become a focal point in this balance between profit and environmental consciousness. These systems were developed as a means for ships to comply with sulfur emissions regulations while continuing to burn High Sulphur Fuel Oil (HSFO), a residual product from oil refining that has historically been the industry’s preferred fuel. Scrubbers offer a way to meet regulatory requirements without switching to more expensive low-sulfur fuels. As a result, they have been widely adopted across the global fleet.

Yet the role of scrubbers is more complicated than it first appears. While they offer a clear compliance pathway under international regulations, they also raise important environmental and local regulatory questions. The technology’s impacts extend beyond its intended purpose of reducing sulfur emissions, particularly in sensitive coastal and marine environments. As directives shift toward broader environmental objectives, the long-term viability of scrubbers is increasingly uncertain. As the industry looks ahead, it’s worth asking: in 2025, with better fuel options available, should we still be designing compliance strategies around burning high‑sulfur fuel oil—arguably one of the dirtiest fuels still in circulation?

In a truly global shipping market, vessels that trade worldwide cannot evaluate compliance in isolation; even occasional calls in regulated waters mean national, regional, and global rules all matter to asset value. For the past five to six years, exhaust gas cleaning systems (scrubbers) often delivered attractive, short payback periods by letting owners burn lower-cost high-sulphur fuel oil. That equation is changing. Rising carbon costs under the EU Emissions Trading System (EU ETS) and FuelEU Maritime amplify the penalty of the additional energy required to operate scrubbers when trading to, from, or within Europe. Looking ahead, the IMO’s emerging mid-term greenhouse-gas measure (often discussed in the context of a global fuel or fuel-intensity standard—“GFI”) could further erode the high-sulphur pathway. At the same time, regional and national restrictions on scrubber wash-water discharge are expanding; the recently adopted OSPAR ban is due to take effect in less than two years, with other ports and coastal states considering similar moves. These policy shifts introduce political/regulatory risk—hard-to- model “unknown unknowns”—on top of the more familiar, but still volatile, “known unknown” of the fuel price spread between high- and low-sulphur grades. To be sure, many of these headwinds matter most to vessels with material EU exposure; a ship that rarely trades in such regimes may find the scrubber case largely intact—at least until the IMO measure comes into force. Given that backdrop, owners should ask whether marginal capital is better deployed into energy-saving technologies: reducing fuel burn cuts operating expenses and emissions everywhere the vessel trades, independent of fuel grade or regulatory boundary.

Environmental Impacts of Scrubber Discharge

The environmental case for scrubbers is closely tied to their role in reducing sulfur emissions. The maritime sector has long been a significant contributor to global air pollution, responsible for an estimated 10% of worldwide sulfur oxide (SOx) emissions. These emissions contribute to ocean acidification, acid rain, and smog, with well-documented impacts on marine ecosystems and human health (Shi et al., 2025).

In response to these risks, the International Maritime Organization (IMO) implemented a global sulfur cap in 2020. The regulation lowered the allowable sulfur content in marine fuels from 3.5% to 0.5%, marking a significant step in controlling emissions from shipping and reducing emissions from the maritime industry by 80%.

Faced with the new standard, shipowners were presented with two main options. The first was to switch to low-sulfur fuels such as marine gas oil (MGO) or very low sulfur fuel oil (VLSFO). The second choice was to install scrubbers to remove sulfur from exhaust gases while continuing to burn HSFO. Economic considerations played a decisive role in many cases. Historically, the price of MGO has been almost twice that of HSFO, though this differential has narrowed somewhat in recent years (Teuchies et al., 2020).

By 2024, over 5,800 ships had installed scrubbers, the majority of which are open-loop systems. These devices spray seawater at the exhaust gasses, dissolving the SOx. The resulting wash water, which contains sulfuric acid, heavy metals, nitrates, nitrites, and polycyclic aromatic hydrocarbons (PAHs), is then discharged into the sea, often at elevated temperatures. These wash water conditions can have serious effects on marine environments, including acidification of local waters, harm to calcifying organisms, bioaccumulation in marine food webs, and nutrient enrichment that may contribute to eutrophication (Hasselöv et al., 2023). Harmful pollutants that would have gone into the air are sent into the ocean instead.

Although scrubber discharges are difficult to quantify precisely, multiple studies have documented their environmental impacts. In a Baltic Sea study, the waste streams traditionally considered the main sources of shipborne pollution, including bilge water from engine rooms, black water or sewage, and grey water from galleys, sinks, and laundry, were compared to the effluent of open-loop scrubbers. They found that the discharge from fewer than 100 scrubbers released between 10 and 100 times more metals and PAHs than the combined waste streams of more than 8,000 ships (Hasselöv et al., 2023).

Laboratory studies reinforce these concerns. Experiments with copepods, which are small crustaceans that form a critical link in marine food webs, have shown that even wash water diluted to just 1% of its original strength can impair survival, growth, and reproduction. At higher concentrations, exposure led to rapid mortality (Hasselöv et al., 2023; Picone et al., 2023). Similar effects have been observed in other plankton populations, suggesting that areas with high ship traffic and limited water exchange face a heightened risk of ecological disruption.

Because plankton are foundational to marine food chains, damage at this level does not remain isolated. Declines in these populations cascade through the ecosystem, reducing food availability for fish and other higher organisms and, ultimately, threatening fisheries and the communities that rely on them. Compounding this, heavy metals and PAHs can bioaccumulate, building up in organisms over time and becoming more concentrated as they move through the food chain. This means contamination introduced at the base of the ecosystem can eventually reach commercially important fish species and even enter the human diet, magnifying the long‑term ecological and public health risks.

Closed-Loop Systems

In response to concerns about open‑loop scrubbers, some advocate for closed‑loop systems as a less harmful alternative. These systems recirculate wash water and treat it onboard with alkalis, such as sodium hydroxide, to neutralize acidity.

While closed‑loop scrubbers reduce some immediate risks, they are not without problems. To accommodate the treatment process, small volumes of wash water are periodically discharged into the ocean—despite the “closed‑loop” label—and these discharges often contain elevated concentrations of pollutants that accumulate during recirculation. The remaining concentrated waste must then be offloaded and disposed of onshore.

Closed‑loop scrubbers are also uncommon, representing less than 2% of the global market, largely due to higher capital and operational costs and the logistical challenges of handling collected waste (Lunde Hermansson et al., 2024). Hybrid systems exist that can switch between open and closed‑loop modes, but the added complexity and cost have limited their adoption. In practice, most shipowners continue to favor open‑loop systems for their lower costs and fewer operational constraints, even though they carry greater environmental risks, underscoring how environmental protection often loses out to cost considerations unless regulations step in.

Climate and Environmental Trade-offs

In addition to their direct marine impacts, scrubbers should also be evaluated for their broader effects on climate and air quality. Some lifecycle assessments suggest that, in certain contexts, scrubbers may perform better than low‑sulfur fuels.

A recent study supported by Oldendorff Carriers examined the full lifecycle impacts of various fuel options for large bulk carriers operating mainly in open‑ocean conditions. The analysis found that ships equipped with scrubbers using HSFO performed as well as, or better than, those burning VLSFO or MGO in several categories, including greenhouse gas emissions, acidification, and ozone formation (Stathatou et al., 2025). These results stem largely from the energy‑intensive refining processes required to produce low‑sulfur fuels.

However, these findings must be interpreted with caution. The study’s scope was limited to vessels operating far from shore, where ocean mixing can dilute pollutants quickly and local ecological risks are relatively low. Globally, scrubbers discharge an estimated 10 gigatonnes of wash water into the ocean each year, and in coastal and high‑traffic areas these discharges are far less diluted. In such regions, pollutants can persist and accumulate over time, raising significant concerns for water quality, biodiversity, and the long‑term health of marine ecosystems (Teuchies et al., 2020; Zis et al., 2022).

A 2018 study found that concentrations of scrubber-related pollutants exceeded the lowest observed effect concentration (LOEC) in parts of the Baltic and North Seas. The LOEC represents the lowest concentration at which harmful effects on marine organisms have been recorded. As shown in Figure 1, exceedances are most common in shallow waters with high vessel traffic. Notably, the waters surrounding Denmark are both shallow and heavily trafficked, increasing the likelihood of pollutant levels reaching thresholds harmful to marine life.

This distinction between environmental impacts and climate effects are often difficult to balance. Lifecycle assessments provide valuable insight into global emissions, however, they do not account for the spatially concentrated effects of scrubber discharges in sensitive marine areas. Global averages can obscure local impacts, and it is important to recognize that reducing greenhouse gas emissions does not necessarily justify introducing harmful pollutants into coastal ecosystems. While the climate footprint of low-sulfur fuels warrants further scrutiny, the immediate and localized harm caused by scrubber discharges, especially in coastal waters, presents a more acute and direct threat to marine environments today.

Additionally, the use of scrubbers gives the industry a continued justification for using HSFO, which may later hurt future decarbonization goals. While the refining process of low-sulfur fuels such as VLSFO or MGO may result in similar or sometimes even higher carbon emissions, they serve as a transitional step. These fuels are more compatible with biofuels and other low-carbon alternatives, which can be gradually introduced through blending. In contrast, HSFO is more difficult to blend because it typically requires pre-treatment or advanced processing to ensure compatibility with biofuels (Hsieh and Felby, 2017).

This tension between short‑term compliance and long‑term sustainability underscores a deeper issue: relying on scrubbers not only locks the industry into continued HSFO use but also perpetuates an outdated mindset about managing pollution. The assumption that the ‘solution to pollution is dilution’ is a familiar but problematic approach in environmental management. Clinging to this logic in 2025 feels increasingly out of step with the scientific consensus and the maritime industry’s stated environmental goals. The United Nations Convention on the Law of the Sea makes clear that “States shall act so as not to transfer, directly or indirectly, damage or hazards from one area to another or transform one type of pollution into another.” Shifting pollution from the air to the ocean is not a viable option if we want to minimize the impact of the maritime industry on the environment. Scrubbers may offer a compliance pathway for sulfur emissions, but they introduce a range of environmental consequences.

Evolving Regulations

While scrubbers remain accepted under current international regulations, their future is becoming more uncertain as environmental priorities broaden beyond sulfur emissions alone. Under MARPOL Annex VI, the IMO permits the use of scrubbers to comply with sulfur limits, provided that ships meet discharge limits on pH, PAHs, turbidity, nitrates, and temperature. However, sampling is inconsistent and is taken after dilution, which does not account for short- term pollutant spikes or cumulative discharges in high-traffic areas. Additionally, the IMO limits are often self-reported by ships, and ineffectively monitored and enforced by ports.

In response, several regional and national authorities have begun imposing restrictions on scrubber discharges by banning their use all together, particularly from open-loop systems. Emission Control Areas (ECAs), such as the North Sea, the Baltic Sea, and the Mediterranean, have increasingly prohibited scrubber discharges to protect local water quality. The most sweeping measure to date came in June of 2025, when the OSPAR Commission announced a ban on scrubber discharges throughout the northeast Atlantic, which is scheduled to take effect in June of 2027 (Hakirevic Prevljak, 2025). This measure will effectively prohibit the use of open-loop scrubbers across large areas of European waters, significantly reducing their operational viability. Although the IMO has not yet adopted a similar global prohibition, the precedent set by OSPAR and mounting evidence of environmental harm have sparked debate within IMO working groups, leaving open the possibility of tighter international limits or future action against open‑loop systems.

Beyond sulfur regulations, European policymakers are now shifting their focus toward carbon emissions, further challenging the business case for scrubbers. Initiatives such as the European Union’s Fit for 55 package and FuelEU Maritime are introducing stricter carbon-related measures, encouraging the adoption of low-emission fuels and energy efficiency technologies. These policies indirectly penalize scrubber-equipped ships because scrubber systems consume additional energy, typically increasing fuel use by 2-10%, and therefore raise ships’ reported carbon emissions.

Beyond sulfur regulations, European policymakers are now shifting their focus toward carbon emissions, further challenging the business case for scrubbers. Initiatives such as the European Union’s Fit for 55 package and FuelEU Maritime are introducing stricter carbon-related measures, encouraging the adoption of low-emission fuels and energy efficiency technologies. These policies indirectly penalize scrubber-equipped ships because scrubber systems consume additional energy, typically increasing fuel use by 2-10%, and therefore raise ships’ reported carbon emissions.

At the same time, the growing availability of biofuels and other low-carbon alternatives is beginning to offer more competitive and scalable solutions. These fuels inherently produce lower levels of sulfur oxides and GHG emissions, positioning them as more compatible with long-term regulatory objectives. Furthermore, energy saving technology, unlike scrubbers, reduces the energy requirement onboard, leading to a lower fuel and regulatory cost. Together, these developments suggest that scrubbers may struggle to retain their role in the maritime industry, particularly in regions where environmental regulations are rapidly evolving.

Changing Economics of Scrubber Investments

In the years immediately following the 2020 sulfur cap, scrubbers offered clear financial advantages for many shipowners. By allowing vessels to continue burning HSFO, scrubbers enabled significant fuel cost savings. In 2019, shipowners collectively saved an estimated €1.7 billion by using scrubbers instead of low-sulfur fuels, with many open-loop systems achieving payback periods of five years or less (Lunde Hermansson et al., 2024).

However, the economics of scrubbers are now shifting in ways that threaten their long-term viability. With carbon penalties increasing under programs such as the EU ETS, and with expanding discharge bans, particularly the forthcoming OSPAR restriction in 2027, the profitability of scrubber installations is diminishing, especially for ships operating in European waters.

For a vessel consuming 20 tons of fuel per day, with an additional 5% fuel consumption attributed to scrubber use, our calculations suggest that installing a scrubber today would likely no longer result in a full return on investment. Without accounting for the 2027 OSPAR ban, the system could still break even in about five years, which is consistent with previous industry estimates. However, as ECAs expand and carbon penalties increase, the economics of scrubbers continue to deteriorate. When factoring in the 2027 OSPAR ban, a variable many earlier assessments overlooked, the payback period was significantly extended for an Atlantic trading vessel, and in some scenarios it would never break even. Despite offering greater flexibility to operate within ECA zones, closed-loop systems face significantly higher upfront and operational costs. As a result, they have even longer payback periods and, under upcoming restrictions, would also fail to recoup the investment.

While these outcomes vary by vessel size, operational patterns, and regional fuel prices, the general trend is clear: scrubbers are becoming less economically attractive in European trade. The most affected ships are those operating on regional routes within or near the northeast Atlantic, where scrubber discharges will soon be prohibited and carbon penalties will apply to the vessel’s emissions.

For those interested in seeing how these calculations were done, or for those who want to adjust the inputs to test other scenarios, please contact us and we will send the excel sheet.

A Transitional Technology

Scrubbers once represented a pragmatic solution during a period of transition in the maritime sector. They provided a relatively quick and cost-effective means for ships to meet sulfur emission standards, especially at a time when high-sulfur fuels dominated the market and low- sulfur alternatives were in limited supply.

However, the context in which scrubbers operate is changing rapidly. The industry’s focus is shifting from sulfur reduction alone to broader environmental protection and decarbonization. New regulations are increasingly targeting carbon emissions alongside traditional pollutants, while expanding regional discharge bans further restrict the areas where scrubbers can be used.

At the same time, the economic equation is shifting. With tightening emission regulations and fuel price spreads narrowing, scrubbers no longer deliver the same financial advantages they once did. In many cases, shipowners face growing risks of stranded assets, especially on vessels operating primarily in Europe. Table 1 summarizes the key issues scrubbers face.

Table 1. Summary of key environmental, regulatory, and economic challenges facing scrubber use in maritime shipping.

Although scrubbers may retain their financial upside on certain long-haul or non-European routes, their widespread use, for both open- and closed-loop configurations, appears increasingly incompatible with the evolving environmental, regulatory, and financial landscape of shipping. This does not take into account any non finalized emissions regulation such as the IMO GFI, nor the risk of further national and regional bans of scrubbers, which also make scrubbers prone to political risks, not just in EU trade. Some industry observers have suggested that scrubbers could potentially be adapted for future applications such as onboard carbon capture, providing a multi-pollutant compliance solution. However, these technologies remain in early development and face significant technical, operational, and cost-related hurdles, while the regulatory framework surrounding onboard carbon capture is unknown to the industry currently.

For now, shipowners must weigh not only regulatory compliance but also broader environmental responsibility and long-term financial risks. As the shipping industry enters a new era of environmental scrutiny and climate accountability, profitability and environmental consciousness are increasingly aligning. It is clear that scrubbers, once seen as a convenient workaround, are evolving into a transitional tool whose time is passing.

Moving towards cleaner fuels and technologies takes time as bunkering infrastructure develops, some engines undergo retrofits, and supply chains adjust. In the short term, many operators will need to plan their routes carefully, phasing out HSFO use in regions with stricter limits while gradually adopting fuels compatible with future decarbonization strategies.

Cooperative industry initiatives, such as joint procurement of biofuels or participation in fuel‑efficiency programs, can smooth this transition. While regulatory pressure is increasing, so too are opportunities for shipowners to stay ahead by investing early in lower‑carbon solutions and route planning that anticipates new ECAs.

Ultimately, the cleanest ton of fuel is the one we never burn. By prioritizing operational efficiency, hull optimization, slow steaming, and cutting the extra fuel consumed by scrubbers, the industry can minimize carbon emissions and regulatory penalties. As directives tighten and public scrutiny grows, this focus on efficiency will not only support environmental stewardship; it will also be central to maintaining profitability in a decarbonizing world.

Table 2. Summary of key assumptions used in economic calculations for each regulatory and compliance scenario.

Sources

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